To support wireless communication between a mobile station and a wireless telecommunications network, multiple frequencies may be used. For example, when frequency division duplexing (FDD) is used, uplink communications (communications from the mobile station to the network) and downlink communications (communications from the network to the mobile station) occur at different frequencies.
The separation between uplink and downlink frequencies may depend on the frequency ranges that are used. As one example, the PCS frequency band that is often used for cellular communications includes an uplink band of 1850-1910 MHz and a downlink band of 1930-1990 MHz. For FDD communications, an uplink carrier frequency in the uplink PCS band is typically paired with a downlink carrier frequency in the downlink PCS band, with a frequency separation between the uplink and downlink carrier frequencies of 80 MHz.
A given pair of uplink and downlink carrier frequencies may be used to support wireless communications with multiple mobile stations in multiple areas. For example, in code division multiple access (CDMA) approaches, the uplink and downlink carriers may be separately modulated with a plurality of different codes to define a plurality of distinct downlink communication channels (such as paging channels and downlink traffic channels) and a plurality of distinct uplink communication channels (such as access channels and uplink traffic channels). The distinct communication channels defined in this way enable communications between multiple mobile stations and the wireless network to occur simultaneously in the same area using only one uplink carrier frequency and one downlink carrier frequency.
In order to increase capacity, wireless telecommunications network are increasingly using multiple uplink carrier frequencies and multiple downlink carrier frequencies in the same wireless coverage area (e.g., a particular cell or sector). As a result, in a given wireless coverage area, some mobile stations may use one pair of uplink and downlink carrier frequencies, while other mobile stations may use a different pair of uplink and downlink carrier frequencies.
It is often desirable to balance the usage of the different carriers that are available. In a conventional approach for load balancing in a given wireless coverage area, the network broadcasts a channel list message (over a paging channel) that identifies the downlink carrier frequencies that are available in that wireless coverage area. Each mobile station operating in the wireless coverage area then uses a selection algorithm to select one of the downlink carrier frequencies. The selection algorithm is typically a hashing algorithm that maps an identifier of the mobile station to one of the downlink carrier frequencies. As a result, the usage of the downlink carrier frequencies available in a given wireless coverage area can be spread out relatively evenly among the different mobile stations operating in the area.
Conventionally, once a mobile station has selected a downlink carrier frequency, the mobile station automatically uses a corresponding uplink carrier frequency, based on the standard frequency separation between uplink and downlink carrier frequencies. For example, when PCS bands are used, the standard frequency separation is typically 80 MHz, as noted above. In this way, the usage of both downlink carrier frequencies and uplink carrier frequencies can be balanced.